This invention relates to an internal combustion engine with an exhaust gas turbocharger and an exhaust gas recirculation device. Preferred embodiments of the invention relate to an internal combustion engine having an exhaust gas turbocharger and an exhaust gas recirculation device, whereby the internal combustion engine has a plurality of cylinders and each cylinder of the internal combustion engine has at least one intake valve and at least one outlet valve, and a compressor of the exhaust gas turbocharger is assigned to an inlet and an asymmetrical exhaust gas turbine of the exhaust gas turbocharger is assigned to an outlet of the internal combustion engine; the compressor is connected to the inlet via a charge air line; the exhaust gas turbine has two intake ports with different flow cross sections that are separated by a partition, each intake port being connected to the outlet through its own exhaust gas inlet line, whereby each exhaust gas inlet line is assigned a partial number of cylinders of the internal combustion engine, and an exhaust gas recirculation line leads from the exhaust gas inlet line of the intake port having the smaller flow cross section to the charge air line.
Supercharged internal combustion engines are known, in particular supercharged diesel engines, which are equipped with an exhaust gas recirculation device to improve exhaust performance. The exhaust gas recirculation by means of the exhaust gas recirculation device reduces NOx emissions in particular. Such internal combustion engines have an exhaust gas turbocharger with a compressor allocated to an inlet and an exhaust gas turbine allocated to an outlet of the internal combustion engine. The exhaust gas turbine and the outlet are connected by at least one exhaust gas inlet line, with an exhaust gas recirculation line of the exhaust gas recirculation device branching off from the exhaust gas inlet line. The exhaust gas recirculation line opens into a charge air line connecting the compressor to the inlet. An exhaust gas recirculation valve is provided in the exhaust gas recirculation line, the exhaust gas recirculation being controllable via this valve.
U.S. Pat. No. 4,179,892 (corresponding German Patent DE 28 55 687 C2) describes an internal combustion engine, the exhaust gas turbine having two separate intake ports (referred to as scroll channels in this publication) and a exhaust gas inlet line (referred to in the publication as an exhaust gas line) being provided for each intake port. The exhaust gas inlet lines connect the intake ports to the outlet of the internal combustion engine. Each exhaust gas inlet line is connected separately from the others to a partial number of cylinders of the internal combustion engine. The intake ports have different flow cross sections. The exhaust gas recirculation line branches off from the exhaust gas inlet line that is provided for the intake port having the smaller flow cross section. The flow cross section of the intake port and/or the exhaust gas inlet line is advantageously selected to be so small that there is a negative purging gradient, so at least some of the exhaust flows through the exhaust gas recirculation line into the charge air line. The recirculated exhaust is distributed uniformly among the cylinders.
The negative purging gradient results in inferior purging and/or an increase in internal exhaust gas recirculation of the cylinders that supply the exhaust gas recirculation device.
It has been found that with a uniform distribution of the recirculated exhaust gas to all the cylinders of the internal combustion engine, the exhaust from the cylinders supplying the exhaust gas recirculation device has a lower NOx concentration and a higher CO concentration in the exhaust than the cylinders that do not supply the exhaust gas recirculation device. The higher CO concentration is an indicator of a low lambda value, which is associated with increased emissions of carbon black and/or particulate matter in diesel engine combustion.
An object of the present invention is to make available an internal combustion engine of the type referred to above, so that the emissions of this internal combustion engine are distributed uniformly over all its cylinders.
This object is achieved according to certain preferred embodiments of the invention by providing an internal combustion engine having an exhaust gas turbocharger and an exhaust gas recirculation device, whereby the internal combustion engine has a plurality of cylinders and each cylinder of the internal combustion engine has at least one intake valve and at least one outlet valve, and a compressor of the exhaust gas turbocharger is assigned to an inlet and an asymmetrical exhaust gas turbine of the exhaust gas turbocharger is assigned to an outlet of the internal combustion engine; the compressor is connected to the inlet via a charge air line; the exhaust gas turbine has two intake ports with different flow cross sections that are separated by a partition, each intake port being connected to the outlet through its own exhaust gas inlet line, whereby each exhaust gas inlet line is assigned a partial number of cylinders of the internal combustion engine, and an exhaust gas recirculation line leads from the exhaust gas inlet line of the intake port having the smaller flow cross section to the charge air line, wherein the distribution of the recirculated exhaust among the individual cylinders of the internal combustion engine is different, whereby a partial number of the cylinders of the internal combustion engine receives all or most of the recirculated exhaust, and the remaining cylinders receive little or none of the recirculated exhaust.
Preferred embodiments of the inventive internal combustion engine are characterized by the different distribution of the recirculated exhaust among the individual cylinders of the internal combustion engine, whereby a partial number of cylinders of the internal combustion engine receive all or most of the recirculated exhaust, and the remaining cylinders receive little or none of the recirculated exhaust. The internal combustion engine has an exhaust gas turbocharger with an asymmetrical exhaust gas turbine. The asymmetrical exhaust gas turbine has two intake ports that have different flow cross sections. One flow cross section is selected to be so small that it results in a negative flow gradient on the partial number of cylinders that are connected to the intake port having the smaller cross section. Therefore, the exhaust from these cylinders can be recirculated by means of an exhaust gas recirculation device. Due to the negative purging gradient, the purging of the cylinders supplying the exhaust gas recirculation is altered so that more exhaust remains in the cylinders supplying the exhaust gas recirculation device and/or flows back into them than into the cylinders that do not supply the exhaust gas recirculation device (internal exhaust gas recirculation). To equalize the ratio of the charge air required for combustion and the exhaust recirculated from the internal exhaust gas recirculation and via the exhaust gas recirculation device among the cylinders of the internal combustion engine, the cylinders that do not supply the exhaust gas recirculation device receive the largest amount of the exhaust recirculated via the exhaust gas recirculation device. The cylinders supplying the exhaust gas recirculation device accordingly receive the smallest amount or none of the exhaust recirculated via the exhaust gas recirculation device. This makes it possible to keep NOx emissions at a required level and to lower CO emissions at the same time, which is reflected in reduced soot emissions and/or particulate emissions.
Advantageous refinements of and improvements on the above discussed preferred embodiments of an internal combustion engine are described herein and in the claims.
In certain preferred embodiments of this invention, the cylinders that do not supply the exhaust gas recirculation device receive the largest amount or all of the recirculated exhaust and the cylinders supplying the exhaust gas recirculation device receive the smallest amount or none of the recirculated exhaust. In an expedient embodiment of this distribution, the cylinders not supplying the exhaust gas recirculation device receive 70% of the exhaust recirculated via the exhaust gas recirculation device. The cylinders supplying the exhaust gas recirculation device receive 30% accordingly.
In certain other preferred embodiments of this invention, the internal combustion engine is designed in the form of an in-line design having four or six cylinders, whereby the partial number of cylinders not supplying the exhaust gas recirculation device amounts to at least half of the cylinders of the internal combustion engine. Due to the negative purging gradient on the cylinders supplying the exhaust gas recirculation device, the efficiency drops, since the purging of the cylinders is inferior. The loss of efficiency can be compensated by optimized charge cycle of the cylinders that do not supply the exhaust gas recirculation device. In order not to have a negative effect on the overall efficiency of the internal combustion engine, the partial number of cylinders supplying the exhaust gas recirculation device is limited to half of the cylinders of the internal combustion engine at most.
In certain other preferred embodiments of this invention, an exhaust gas recirculation valve in the form of a throttle valve is provided in the exhaust gas recirculation line. The exhaust gas recirculation valve is controllable by means of a signal line of a control unit of the internal combustion engine. The exhaust gas recirculation can thus be controlled by means of the exhaust gas recirculation device and can be adapted to an engine characteristics map of the internal combustion engine.
In certain other preferred embodiments of this invention, the valve control times of the intake valves and/or the outlet valves of the individual cylinders of the internal combustion engine are different, whereby the cylinders supplying the exhaust gas recirculation device have shorter valve overlap times or none at all in comparison with the cylinders that do not supply the exhaust gas recirculation device. The valve control times of the intake valves and the outlet valves in internal combustion engines usually have a valve overlap, i.e., the intake opens before the outlet closes. Due to this valve overlap, there is internal exhaust gas recirculation, in particular when there is a negative purging gradient. Due to opening of the intake, the pressure in the cylinder space drops below the exhaust gas pressure and exhaust gas remains in the cylinder space or flows back out of the outlet. The degree of internal exhaust gas recirculation can be influenced with the design of the valve overlap times and decreases with shortening of the valve overlap times in an advantageous manner.
In certain other preferred embodiments of this invention, the valve control times of the intake valves of the cylinders supplying the exhaust gas recirculation device are retarded. The valve control times are advantageously retarded by five degrees of crank angle with a uniform valve lift diagram.
Other features and combinations of features are derived from the description and the drawing. A concrete exemplary embodiment of this invention is shown in simplified form in a drawing and explained in greater detail in the following description.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.